1. Field of the Invention
The present invention relates to a replaceable cutting tool for drills, end mills, and milling cutters and a throw-away insert used as a blade therefor.
2. Description of the Background Art
Throw-away inserts primarily belong to two main groups: the type described in the JIS handbook (JIS B4120), i.e., the negative type, having parallel upper and lower surfaces with side surfaces intersecting at 90 degree angles; and the positive type, where the side surfaces form acute angles with the upper surface and obtuse angles with the lower surface. In negative throw-away inserts, the upper and lower surfaces are identical, so that the sides of the upper surface (the ridge lines formed by the intersections with the side surfaces) and the sides of the lower surfaces can be used as cutting sections, making the structure economical. While the cutting edge is strong, negative inserts do not provide clean cuts and the cutting force is high.
With positive throw-away inserts, cuts are clean and cutting force is low, but the strength of the cutting edge is less than that of negative inserts, and there are fewer usable corners for cutting.
FIG. 19 shows another type of throw-away insert. In this “longitudinal-use” throw-away insert, a side surface 53 serves as the rake face, and a ridge line 54, where upper and lower surfaces 51, 52 intersect with the side surface 53 serves as the cutting section.
This type of throw-away insert is used for pin milling cutter, in which strength is important. However, the narrow area of the rake face makes it difficult to improve chip handling, and cutting force also tends to be high.
Conventional throw-away inserts are used for single functions, forcing trade-offs of advantages and disadvantages as described above. The object of the present invention is to provide a multi-functional throw-away insert. More specifically, the object of the present invention is to: allow use of a longitudinal-use structure while providing functions similar to those of positive and negative inserts; provide improved cutting edge strength, improved cleanness of cut, and reduced cutting force; and increase the number of usable corners.